import java.util.Scanner;

public class ZY5 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("请输入钢管长度：");
        double a = input.nextDouble();
        double b = (int) a / 3, c = a % 3, d = b + 1;
        if (c == 0) {
            System.out.println("需要买" + b + "根钢管。");

        } else {
            System.out.println("需要买" + d + "根钢管。");
        }
    }
}
